The present invention relates to bowstrings for archery bows which are made from a plurality of high strength strands which are a blend of at least two fibers, some of the fibers being made of a first material and some of the fibers being made of a second material. The blend of fibers results in a bowstring having high tensile strength and good creep resistance.
The bow and arrow is one of the earliest weapons conceived by man and have been in use for tens of thousands of years. In its simplest form the bow was a bent stick that was held in the bent condition by having a string of somewhat shorter length attached to either end. By holding this braced stick in one hand, one could place one end of a second straight stick against the string and by pulling both the stick and string away from the bow hand and releasing, could launch the second stick. Over the years there have been great advances in the development of the bow, composite bows, composite recurve bows, and state of the art compound bows that represent different stages of bow sophistication.
Similarly, there have been advances in the materials used for making bowstrings. Some of the earliest bowstrings were manufactured from animal fibers such as sinew. Later, bowstrings were manufactured from other fibers such as flax or linen.
In the last century, bowstrings have been most commonly manufactured from manmade fibers with DACRON(copyright) polyester available from DuPont being the most popularly used material through the later 1980""s. DACRON(copyright) B-50 was the most commonly used of the DACRON(copyright) fiber materials with the xe2x80x9c50xe2x80x9d being used to refer to a single strand breaking strength (tensile strength) of about 50 pounds. This material exhibited very consistent mechanical properties and performance, had good abrasion resistance, and exhibited durability when used in bowstrings.
The popularity of DACRON(copyright) bowstrings decreased, however, with the appearance of KEVLAR(copyright) poly-paraphenylene terephthalamide (aramid fiber), another popular synthetic material used in the 80""s and also available from DuPont. KEVLAR(copyright) exhibited a higher tensile strength at break and thus higher breaking strength per strand, and also had a much higher modulus of elasticity as compared to DACRON(copyright) which resulted in improved performance characteristics, and the higher tensile strength allowed a reduced number of strands which more than compensated for its higher density. Lighter mass weight technically results in a higher arrow launch velocity. However, KEVLAR(copyright) exhibited a limited life expectancy, sometimes producing only 1000 to 1500 shots per string, the use of KEVLAR(copyright) was predominantly limited to traditional bows specifically designed for use with KEVLAR(copyright) bowstrings, and its use was limited to a relatively small number of top level tournament archers due to its low resistance to cyclic bending.
In the later 1980""s a new synthetic string material came on the scene, this material was made from SPECTRA(copyright) 1000 ultra high molecular weight polyethylene fiber available from the High Performance Fibers Group of AlliedSignal, Inc. Bowstrings material manufactured of SPECTRA(copyright) polyethylene is available from Brownell under the tradename of FAST FLIGHT(copyright).
U.S. Pat. No. 4,957,094 entitled COMPOUND ARCHERY BOW WITH NON-STRETCH BOWSTRING AND ECCENTRICS FOR SECURING THE SAME describes bowstrings and cable harnesses manufactured from SPECTRA(copyright).
The SPECTRA(copyright) fiber was also a very high strength fiber with a very high modulus of elasticity and a density less than the fiber used in DACRON(copyright) B-50. This material, in addition to being lightweight, and having high strength and high modulus, also exhibits excellent durability and excellent abrasion resistance. Significantly improved performance was exhibited by bows using SPECTRA(copyright) 1000 (FAST FLIGHT(copyright) bowstrings) as compared to DACRON(copyright) B-50 bowstrings with one particular improvement being higher arrow launch velocity exhibited with the SPECTRA(copyright) made bowstrings.
However, SPECTRA(copyright) material is subject to creep. Creep or stretch of the bowstring is a typical problem encountered by archers using the SPECTRA(copyright) made bowstrings. When the bow is subject to a load, both when holding the bow in the brace condition and when the bowstring is drawn and released for arrow propulsion, the string elongates in proportion to the load applied. For many materials, the string returns to its original length once the load is removed. If a material exhibits creep, however, the string does not fully return to its original length, and the string will elongate or stretch permanently over a given period of time. Time, temperature, and the applied load can influence the rate and severity of the stretching due to creep. This obviously affects the performance of the bow.
Another ultra high molecular weight polyethylene is sold under the tradename of DYNEEMA(copyright) available from DSM-Toyobo, which is made by a different process than SPECTRA(copyright). This polymer, however, also exhibits lower resistance to creep.
Since the appearance of SPECTRA(copyright) there have been several other new synthetic fibers introduced which have been utilized in the manufacture of bowstrings. Examples of these materials include VECTRAN(copyright) liquid crystal polymer (LCP) available from Hoechst Celanese Corp. and ZYLON(copyright) poly(p-phenylene-2-6-benzobisoxazole) available from Toyobo Co.
VECTRAN(copyright) does not exhibit poor creep characteristics as compared to SPECTRA(copyright) and provides high tensile strength and modulus. However, VECTRAN(copyright), like KEVLAR(copyright), also suffers from lower abrasion resistance and a short life expectancy, but to a lesser degree than the latter. Another disadvantage of VECTRAN(copyright) is that it has a lower modulus of elasticity than SPECTRA(copyright) which ultimately results in lower arrow velocities than can be achieved with SPECTRA(copyright).
ZYLON(copyright) is made up of rigid rod chain molecules of poly (p-phenylene-2,6-benzobisoxazole) (PBO). ZYLON(copyright) fibers exhibit some of the he best mechanical properties available and have high strength, high modulus, and no negative creep characteristics. However, to date, there is little experience with the material for use in bowstrings. One disadvantage that has been observed with the ZYLON(copyright) material itself is that its strength is severely affected by sunlight. This may restrict its use in bowstrings. To date, there has been no single material that achieves the desired level of performance when used in a bowstring. Each material exhibits a particular weakness or weaknesses.
Attempts have therefore been made to combine materials in order to achieve the desired characteristics. One attempt resulted in bowstrings referred to as xe2x80x9cKEVDACxe2x80x9d which referred to the fact that they were made up of individual strands of KEVLAR(copyright) and DACRON(copyright), each string being composed of an equal number of strands of each material. This resulted in a string wherein the worst properties of both materials were exhibited. Strings made of KEVDAC(copyright) did not significantly improve arrow launch velocity and exhibited the short life expectancy of KEVLAR(copyright).
Another attempt used a blended material, xe2x80x9cS4xe2x80x9d, wherein SPECTRA(copyright) polyethylene and VECTRAN(copyright) LCP were actually blended at a 50/50 ratio at the fiber level rather than at the strand level. These strings did not exhibit any negative creep characteristics but their life expectancy was still relatively short and somewhat unpredictable.
These materials have also been blended at a ratio of 68% SPECTRA(copyright) polyethylene to 32% VECTRAN(copyright) LCP and marketed under the tradename of xe2x80x9c450 Plusxe2x80x9d. However, this blend still did not achieve the level of dynamic performance exhibited by a bowstring manufactured only of SPECTRA(copyright), although it had a reasonable life expectancy and no negative creep characteristics.
U.S. Pat. No. 5,884,617 describes bowstrings constructed of braided strands, preferably comprising flat braids, from a high strength mixture of yams comprising abrasion-resistant fibers and yams comprising high strength, creep resistant fibers.
The present invention relates to a bowstring for an archery bow that exhibits improved properties such as good life expectancy, negligible creep, and enhances bow performance.
In the broadest sense, the present invention relates to a bowstring made up of a plurality of strands each strand made of at least two different fibers, each fiber having a minimum modulus of elasticity of about 8,000,000 psi and a minimum ultimate tensile of about 350,000 psi.
More particularly, the present invention relates to a bowstring which is about 10 wt-% to 30 wt-% liquid crystal polymer and 70 wt-% to about 90 wt-% ultra high molecular weight polyolefin.
More particularly, the present invention relates to a bowstring made of a plurality of strands each strand being made of a blend of at least two different fibers. The bowstring is of a composition such that about 10 wt-% to 30 wt-% of the bowstring is liquid crystal polymer and 70 wt-% to about 90 wt-% of the bowstring is ultra high molecular weight polyolefin.
The present invention further relates to an archery bow having a bowstring of the present invention, and more particularly, the present invention relates to an archery bow having a handle portion, upper and lower limbs having outside ends, the limbs attached to the handle portion and extending outwardly therefrom with the outside ends, and a bowstring attached to the outside ends made of a plurality of strands each strand made of a blend of at least two fibers. The resultant bowstring is about 10 wt-% to 30 wt-% liquid crystal polymer and 70 wt-% to about 90 wt-% ultra high molecular weight polyolefin.
The bowstring may be attached to the outside ends using any means known to those of skill in the art.
The archery bow may be a compound bow, and may further include a pair of rotation members rotatably mounted on the outer ends of each limb, the bowstring extending between the rotation members.